1. Field of the Invention
The present invention relates generally to a fluid-filled elastic mount adapted to provide a vibration damping effect on the basis of flows of a fluid filling the fluid chamber thereof. More particularly, the present invention is concerned with such a fluid-filled elastic mount that is novel in construction and which is suitably used as an engine mount, a body mount or other mounts for an automotive vehicle.
2. Description of the Related Art
As one type of a vibration damping device such as a vibration damping coupling (bushing) or mount, which is interposed between two members of a vibration system for flexibly connecting these two members or mounting one of these members on the other member in a vibration damping manner, there is known a fluid-filled elastic mount wherein a first metallic mounting member and a second metallic mounting member having a hollow cylindrical configuration are spaced apart from each other such that the first mounting member is disposed on the side of one of opposite open ends of the second mounting member, and are elastically connected to each other by an elastic body, whereby the one open end of the second mounting member is fluid tightly closed by the elastic body. The other open end of the second mounting member is fluid tightly closed by a flexible rubber diaphragm, to thereby define a fluid chamber between the elastic body and the flexible diaphragm, which is filled with a non-compressible fluid. The fluid-filled elastic mount further includes a metallic partition member supported by the second mounting member, which is adapted to divide the fluid chamber such that a pressure-receiving chamber which is partially defined by the elastic body is formed on one side of the partition member, while a variable-volume equilibrium chamber which is partially defined by the flexible diaphragm formed on the other side of the partition member. These pressure receiving and equilibrium chambers communicate with each other by an orifice passage. Upon application of vibrational loads between the first and second mounting members, a pressure of the fluid in the pressure receiving chamber changes due to elastic deformation of the elastic body, generating a pressure difference of the fluid between the pressure receiving and equilibrium chambers. Based on this pressure difference of the fluid, the non-compressible fluid forcedly flows through the orifice passage between the pressure receiving and equilibrium chambers, so that the fluid-filled elastic mount can exhibits an excellent vibration damping effect, owing to resonance or flows of the fluid flowing through the orifice passage. In the light of this excellent vibration damping effect, the elastic mount of this type is favorably used as an engine mount or a body mount for an automotive vehicle, for example.
Such a fluid-filled elastic mount can exhibit a desired vibration damping effect based on the resonance or flows of the fluid flowing through the orifice passage, by suitably tuning or determining a length and a cross sectional area of the orifice passage. In order to exhibit the excellent vibration damping effect of the elastic mount, the orifice passage needs to be made longer enough to assure a sufficiently large amount or mass of the fluid flowing through the orifice passage. To this end, the orifice passage may be conventionally constructed by using the partition member and an annular closure member made of metal, which is bonded at its outer peripheral portion to the periphery of the flexible diaphragm upon vulcanization of a rubber material for forming the flexible diaphragm. The annular closure member and the partition member are superposed on each other and fixed by calking at their peripheral portions to the other open end portion of the second mounting member which is remote from the first mounting member, to thereby define therebetween an annular passage extending in the circumferential direction thereof. The annular passage includes a partition wall formed at a circumferential portion thereof so as to fluid-tightly divide the annular passage in the circumferential direction, and a first and a second communication hole located on the opposite sides of the partition wall, so that the annular passage is held in fluid communication through the first and second communication hole with the pressure receiving chamber and the equilibrium chamber, respectively, thereby providing the orifice passage. According to this conventional structure of the orifice passage, the orifice passage is effectively and easily formed at the radially outward portion of the fluid chamber, so as to extend in the circumferential direction of the second mounting member with a circumferential length which is slightly smaller than the circumference of the second mounting member.
However, the conventional orifice structure may possibly suffer from a problem of insufficient fluid tightness at the partition wall portion, resulting in undesirable fluid communication between both ends of the orifice passage located on the opposite sides of the partition wall. This drawback makes it impossible to obtain a desired length of the orifice passage, resulting in deterioration of the vibration damping effect of the elastic mount.
To cope with the conventionally experienced problem, the present assignee has proposed an improved orifice structure as disclosed in JP-A-8-128491, wherein a partition wall made of an elastic body is formed at a circumferential portion of the annular passage so as to protrude from the partition member toward the closure member with a radial length which is reduced in a direction toward the closure member. That is, the partition wall has an inclined outer circumferential surface. The closure member is also arranged to have an inclined inner circumferential surface corresponding to the inclined outer circumferential surface of the partition wall. The inclined inner circumferential surface of the closure member is superposed on and forcedly pressed against the inclined outer circumferential surface of the partition wall, owing to the calking force applied between the partition and closure members. The inclined inner circumferential surface of the closure member which defines outer circumferential surface of the orifice passage inevitably causes undesirable reduction in the cross sectional area of the orifice passage, possibly leading to difficulty in assuring a required insufficient vibration damping effect of the elastic mount. Thus, the conventional fluid-filled elastic mount as descried above, still has some room for improvement.
It is therefore an object of the invention to provide a fluid-filled elastic mount which is novel in construction and which permits an easy formation of an orifice passage that is partially defined by and between a partition member and a closure member which are superposed on each other and fixed by calking to a second mounting member. The orifice passage extends in the circumferential direction of the partition and closure members with a circumferential length slightly smaller than a circumference of these members and with a sufficiently large cross sectional area. The orifice passage also exhibits an excellent fluid-tightness at a partition wall portion, thereby preventing undesirable fluid-leakage or fluid-communication between both ends of the orifice passage located on the opposite sides of the partition wall.
The above object of the invention may be achieved according to the principle of the invention, which provide a fluid-filled elastic mount including (a) a first mounting member and a generally cylindrical second mounting member, which are spaced apart from each other in an axial direction of the second mounting member, (b) an elastic body elastically connecting the first and second mounting members so as to fluid-tightly close one of axially opposite open ends of the second mounting member, (c) a partition member made of metal and extending in a direction perpendicular to the axial direction, (d) a closure member made of metal and having a central through hole and a flexible diaphragm fluid-tightly closing the central through hole, the partition member and the closure member being superposed on each other and fixed at their peripheral portions to the other of axially opposite open ends of the second mounting member, by calking, so as to provide on one of opposite sides of the partition member a pressure receiving chamber which is partially defined by the elastic body and filled with a non-compressible fluid, and on the other of opposite sides of the partition member an equilibrium chamber which is partially defined by the flexible diaphragm and filled with the non-compressible fluid, and (e) an orifice passage for fluid communication between the pressure receiving chamber and the equilibrium chamber, the orifice passage being formed between the partition and closure members so as to extend in a circumferential direction of the partition and closure members, wherein an improvement comprises: the partition member including an axial protrusion formed at a radially intermediate portion thereof and having an outer circumferential surface extending in the circumferential direction thereof, and a cylindrical positioning shoulder located radially inwardly of the peripheral portion thereof, the closure member including an integrally formed cylindrical wall portion located radially inwardly of and protruding axially outwardly from the peripheral portion thereof, and an integrally formed annular plate portion extending radially inwardly from a protruding open end portion of the cylindrical wall portion, the partition and closure members being superposed on each other such that the cylindrical wall portion of the closure member is partially press-fitted onto an outer circumferential surface of the cylindrical positioning shoulder of the partition member so as to be positioned relative to the partition member in a diametric direction thereof, and that the annular plate portion of the closure member being superposed at an inner peripheral portion thereof on a protruding end face of the axial protrusion of the partition member to thereby provide an annular passage partially defined by and circumferential extending between the cylindrical wall portion of the closure member and the axial protrusion of the partition member which are opposed to each other in the diametric direction, the annular groove including a partition wall formed at a circumferential portion thereof, the partition wall protruding radially outwardly from the side of the partition member toward the side of the closure member such that the partition wall is elastically pressed against the side of said closure member to thereby fluid tightly intercept the annular passage in a circumferential direction thereof; and the annular passage being held in fluid communication with the pressure receiving chamber through a first communication hole formed on one of circumferentially opposite sides of the partition wall and with the equilibrium chamber through a second communication hole formed on the other side of the partition wall, to serve as the orifice passage.
In the fluid-filled elastic mount of the present invention constructed as described above, the partition and closure members are superposed on and assembled with each other in the axial direction such that the cylindrical wall portion of the closure member is press-fitted onto the positioning shoulder of the partition member, so that the partition and closure members are fixed by calking to the second mounting member with these members positioned relative to each other in a substantially coaxial or concentric relationship. In this condition, the suitably dimensioned outer circumferential surface of the partition wall of the partition member and the suitably dimensioned inner circumferential surface of the cylindrical wall portion of the closure member are elastically pressed against each other with the partition wall compressed in the radial direction by a predetermined compression amount. Therefore, the engine mount of the present invention effectively and stably assures that the partition wall is held in elastically pressing contact at its outer circumferential surface with the inner circumferential surface of the outer cylindrical wall portion, without needing a specific operation for positioning the partition and closure members relative to each other in the diametric direction. In addition, with the thus assembled partition and closure members being fixed by calking to the second mounting member, an axial compression force caused by the calking acts on the interfaces between an axially protruding end face of the partition wall of the partition member and the annular plate portion of the closure member, so that the partition wall and the annular plate portion of the closure member are pressed against each other with high stability.
That is, the present engine mount assures the pressing contact of the partition wall with the cylindrical wall portion of the closure member with high stability, in the condition where the cylindrical wall portion of the closure member being press-fitted onto the positioning shoulder of the partition member, without requiring the specific operation for positioning the partition and closure members relative to each other in the diametrical direction. This makes it possible to substantially completely eliminate the conventionally experienced problem of the undesirable fluid-leakage or communication between both ends of the orifice passage, resulting in desired vibration damping effect of the engine mount based on the flows of the fluid flowing through the orifice passage, with high stability.
According to one preferred form of the present invention, the first and second communication holes are formed on the side of the partition member. This makes it possible to eliminate a requirement for positioning the partition and closure members relative to each other in the circumferential direction, leading to further improved efficiency of assembling the partition and closure members. For instance, the first communication hole may be effectively constituted by a through hole formed through the partition member, which is located on one of opposite sides of the partition wall in the circumferential direction, and which is also located radially inwardly of the positioning shoulder. This through hole allows one of circumferentially opposite ends of the orifice passage to communicate with the pressure-receiving chamber, thereby functioning as the first communication hole. The second communication hole, for example, may be effectively constituted by a small-diameter portion of the annular protrusion located on the other side of the partition wall. Namely, the outer circumferential surface of the axial protrusion, which partially defines an inner circumferential surface of the orifice passage, is partially retracted radially inwardly at a circumferential portion located on the other side of the partition wall. The small diameter portion of the annular protrusion allows the other end of the orifice passage to communicate with the equilibrium chamber, thereby functioning as the second communication hole.
In the present invention, the positioning shoulder of the partition member may possibly be formed of a rubber material, a resin material or other suitable materials, and fixedly secured to the partition member. Preferably, the positioning shoulder is integrally formed with the partition member. The positioning shoulder formed as an integral part of the partition member made of metal, permits a higher degree of stability and precision of the positioning of the partition and cylindrical members relative to each other, in comparison with the positioning shoulder formed of the elastic body or the resin material, resulting in a further improved degree of reliability in preventing the mutual communication between the both ends of the orifice passage.
According to another preferred form of this invention, the partition and closure members are both formed of a metallic material by pressing. This arrangement assures an improved efficiency and reduced cost of manufacture of these two members. For instance, the partition and closure members may be effectively formed of a ferrous metal or other metallic materials such as an aluminum alloy. Further, any other suitable operations other than the pressing operation may be employed for forming the partition and closure members.
According to a further preferred form of this invention, the partition member further includes a central through hole and an elastic movable plate fluid-tightly closing the central through hole, the elastic movable plate being elastically deformable based on a fluid pressure difference between the pressure receiving and equilibrium chambers, which fluid pressures act on opposite surface of the elastic movable plate, respectively. This elastic deformation of the elastic movable plate functions to offset or absorb the fluid pressure change in the pressure receiving chamber, upon application of the high frequency vibrations causing a substantially no flow of the fluid flowing through the orifice passage. In the presence of the elastic movable plate, the elastic mount according to this preferred form of the invention can exhibit an improved vibration damping effect with respect to the high frequency vibrations.
According to a still further preferred form of the present invention, the axial protrusion of the partition member is formed of a rubber material, and the partition wall is integrally formed with the axial protrusion. In this preferred form of the invention, the axial protrusion and the partition wall are formed as an integral elastic body. This arrangement is effective to provide the orifice passage which exhibits an improved fluid-tight sealing, and which is free from the problem of the fluid-leakage or fluid-communication between the both ends of the orifice passage, with high stability. In this case, the axial protrusion preferably includes a reinforcing plate embedded therein and formed as an integral part of the partition member, in order to assure desired stability and rigidity of the axial protrusion. When the partition member includes the elastic movable plate according to the aforementioned preferred form of the invention, preferably, the elastic movable plate is also integrally formed with the axial protrusion and the partition wall.
According to a yet further preferred form of this invention, there is provided a sealing rubber layer which is bonded to inner circumferential surfaces of the cylindrical wall portion and the annular plate portion of the closure member, and which is integrally formed with the flexible diaphragm, the closure member being press-fitted at the cylindrical wall portion thereof to the cylindrical positioning shoulder of the partition member via the sealing rubber layer, and being press-fitted at the annular plate portion thereof to the protruding end face of the axial protrusion of the partition member via the sealing rubber layer, the partition wall of the partition member being pressed against or being held in pressing contact with the closure member via the sealing rubber layer.
In this preferred form of the present invention, a clearance possibly formed between the partition and closure members due to the dimensional tolerances of the partition and closure members, is effectively absorbed by the sealing rubber layer interposed between and compressed by the partition and closure members, resulting in further improved fluid-tight sealing of the orifice passage. Preferably, the sealing rubber layer is used together with the axial protrusion and the partition wall, which are formed as the integral elastic body as in the aforementioned preferred form of the invention.
The positioning shoulder may have a generally cylindrical outer circumferential surface extending in the axial direction with a generally constant diameter. Alternatively, the positioning shoulder may have a tapered outer circumferential surface extending in the axial direction with a diameter gradually reduced in the axially extending direction thereof. In the latter case, the tapered positioning shoulder may further facilitate the operation for press-fitting the cylindrical wall portion of the closure member to the positioning shoulder. In the farmer case, the generally cylindrical outer circumferential surface may preferably be arranged to have a rounded edge at its protruding end face, so that the outer circumferential surface of the positioning shoulder functions as a guide surface along which the cylindrical wall portion of the closure member is pushed toward the partition member, upon press-fitting the closure member to the partition member.
According to a still yet further preferred form of this invention, the partition wall formed in the partition member may be dimensioned such that the outer circumferential surface of the partition wall is aligned in the axial direction with the outer circumferential surface of the positioning shoulder, or alternatively is retracted radially inwardly from the outer circumferential surface of the positioning shoulder with a slight amount of radial distance. Namely, the outer circumferential surface of the partition wall is located not to protrude radially outwardly from the outer circumferential surface of the cylindrical positioning shoulder. The cylindrical wall portion includes a local portion adapted to contact with the outer circumferential surface of the partition wall and protruding radially inwardly from the outer circumferential surface of the cylindrical positioning shoulder, so as to be elastically pressed against or to be held in pressing contact with the outer circumferential surface of the partition wall in the radial direction of the partition and closure members.
In this preferred form of the invention, a mold used for forming the partition wall by vulcanizing a rubber material, never has an overhang, resulting in improved efficiency in vulcanizing and pressing operations for manufacturing the partition and closure members.